PAIN Flashcards
What is pain?
- an unpleasant sensory & emotional experience
- a/w actual/potential tissue damage
Classification of pain? (duration & pathophysiology)
Duration
- acute
- chronic
- breakthrough
Pathophysiology
- nociceptive (split into somatic & visceral)
- neuropathic
Diff between acute and chronic pain? (in terms of onset)
Acute: recent onset & probable limited duration
Chronic: last >3-6m or persists beyond duration of an acute disease, or after tissue healing is complete
Diff between acute and chronic pain? (in terms of type of pain)
Acute: nociceptive usually, but can be neuropathic
Chronic: nociceptive, neuropathic or both
Diff between acute and chronic pain? (in terms of sx)
Acute: sharp, dull, shock-like, tingling, shooting, radiating, fluctuating in intensity, varying in location (timely r/s with obvious noxious stimuli)
Chronic: same as acute but no timely r/s, pain stimulus may cause sx that completely change (e.g. sharp to dull)
Diff between acute and chronic pain? (in terms of signs)
Acute: can cause HTN, tachycardia, diaphoresis, mydriasis, pallor
Chronic: comorbid conditions often present, whatever listed in acute is seldom present
Diff between the cause of neuropathic and nociceptive pain?
Neuropathic: caused by lesion / disease of somatosensory nervous system
Nociceptive: arises from actual / threatened damage to non-neural tissue, due to activation of nociceptors in an individual with a normally functioning somatosensory nervous system
Features of neuropathic, somatic & visceral pain?
Where somatic & visceral pain arise from, characteristics of each pain
Neuropathic: burning, sharp stabbing pain, like electric shock (hyperalgesia or allodynia)
Somatic: arise from damage to body tissues, sharp / hot / stinging, localised
Visceral: arise from viscera mediated by stretch receptors (from internal organs), usually accompanied by N/V
What is hyperalgesia and allodynia?
Hyperalgesia: exaggerated painful responses to normally noxious stimuli
Allodynia: painful responses to normally non-noxious stimuli
What is SOCRATES used for and what does it stand for?
Used for pain hx taking
Site
Onset
Characteristics
Radiation
Associated sx
Time course
Exacerbating / relieving factors
Severity
What are the pain scores used to assess pain?
- numeric rating scale
- verbal descriptor scale
- faces pain scale
What is the pain ladder from WHO?
- non-opioid +- adjunvant
- opioid for mild-moderate pain +- non-opioid +- adjuvant
- opioid for moderate-severe pain +- non-opioid +- adjuvant
What are non-opioids?
Paracetamol, NSAIDs
What are weak and strong opioids?
Weak: tramadol, codeine etc
Strong: morphine, fentanyl etc
When is paracetamol absolutely CI and cautioned in?
CI: Liver failure
Caution: hepatic insufficiency, chronic alcohol abuse or dependence
When is NSAIDs CI?
- GI ulcer/bleed
- asthma
- pregnancy 3rd trimester
- kidney problem
- CVD (uncontrolled HTN, HF, IHD)
- allergy
- liver problem
- bleeding disorder / meds
What are the greatest risk a/w COX-1 and COX-2 inhibition activity?
COX-1: upper GI bleed/perforation
COX-2: CVD
Do NSAIDs help with non-specific low back pain?
No
Is celecoxib or etoricoxib more COX-2 selective?
Etoricoxib
Selectivity from COX-1 to COX-2? (12 drugs)
Ketoprofen, piroxicam, indometacin, aspirin, naproxen, ibuprofen, diclofenac, mefenamic acid, meloxicam, celecoxib, parecoxib, etoricoxib
NSAIDs MOA?
Block COX (which breaks down AA to prostaglandins TXA2, PGE2, PGI2)
Function of PGI2, PGE2 and TXA2?
PGI2: vasodilation, inhibit platelet aggregation
PGE2: vasodilation, vasoconstriction, vascular permeability (swelling), pain
TXA2: vasoconstriction, platelet aggregation
MOA of codeine?
weak mu & delta opioid agonist -> metabolised to morphine by CYP2D6
MOA of tramadol?
weak mu opioid agonist & inhibit reuptake of NA & serotonin
When should dose of tramadol be reduced?
≥75y, hepatic+/ renal impairment (lower seizure threshold)
Is morphine more or less constipating than fentanyl?
More constipating
What is the active metabolite of morphine? What happens in renal impairment?
Morphine-6-glucuronide, accumulates and cause more SE
How often should fentanyl patch be changed? How long does fentanyl stay effective after removal of the patch? Does fentanyl patch work immediately?
Q72h
Stays effective for up to 12h after removal
Does not work immediately, takes 10-18h
Lowest dose of fentanyl patch? Can the patch be cut to give the lower dose?
6mcg/hr (half of 12mcg patch)
Cannot cut patch, peel off half of the backing and paste on skin
Common SE of opioids? (9)
Constipation, drowsiness, N/V, dry mouth, urinary retention, delirium, itch/rash, hyperalgesia, resp depression
To prevent opioid-induced constipation, what should the pt be given?
2 REGULAR laxatives (Senna, lactulose)
Conversion between diff opioids?
- codeine:morphine
- tramadol:morphine
- oxycodone:morphine
- fentanyl:morphine
- morphine SC:morphine PO
- fentanyl PO: fentanyl TD
- codeine:morphine = 10:1
- tramadol:morphine = 5:1
- oxycodone:morphine = 2:1
- fentanyl:morphine = 100:1
- morphine SC:morphine PO = 3:1
- fentanyl PO: fentanyl TD = 1:1
What units is fentanyl patch?
mcg
If pain was effectively controlled and pt is opioid tolerant, what should be done to the dose after conversion? Why?
Reduce dose by 25-50% to allow for incomplete cross tolerance b/w opioids
If previous dose was ineffective, what should be done to the dose?
Keep at 100% or up to 125% of prev dose
What can be used for neuropathic pain?
Gabapentin, pregabalin, amitriptyline, nortriptyline, topical lidocaine
What kind of pain can corticosteroids be used for?
- bone pain
- neuropathic pain
- raised intracranial pressure
- liver capsule stretch pain
What can be used for bone pain?
Bisphosphonates
What can be used for cramps / muscle spasm?
Muscle relaxants (e.g. baclofen), benzodiazepines
What can be used for intestinal colic?
Hyoscine butylbromide
Can aspirin be used in <16y? Why?
No, due to risk of Reyes syndrome
Which NSAID has a lower risk of cardiovascular toxicity than the rest?
Naproxen
What is the difference between naproxen sodium and naproxen base?
Naproxen sodium has more rapid absorption & onset of effect than naproxen base
Up to how often can topical pain preparations be applied? Any exceptions?
up to QDS
EXCEPT ketoprofen & diclofenac patch (only 2 patches in 24h)
1st lines for neuropathic pain?
- amitriptyline
- duloxetine
- gabapentin
- pregabalin
What is topical capsaicin used for?
Neuropathic pain
1st line for trigeminal neuralgia? Other possible treatments?
1st line: Carbamazepine
Others: lamotrigine, gabapentin, pregabalin
When can tramadol be used for neuropathic pain?
If acute rescue therapy is needed
Can gabapentin/pregabalin be used in pregnancy?
Not recommended
Nonpharm for pain?
- exercise, posture
- superficial heat
- cryotherapy
- transcutaneous electrical nerve stimulation (TENS)
- massage
How do NSAIDs cause AKI?
- inhibit PGE2: increase Na & water retention -> peripheral edema, HTN
- inhibit PGI2: suppress RAAS -> less K excretion -> hyperK
- vasoconstriction of afferent arteriole -> reduce renal perfusion
NSAIDs SE?
- GI ADR (dyspepsia, N/V, anorexia, abd pain, ulcers)
- renal ADR (AKI)
- pseudo-allergic reaction (excess leukotrienes from inhibiting COX)
- asthma (excess leukotrienes from inhibiting COX)
- bleeding
- reproduction ADR (CI in 3rd trimester of pregnancy due to premature closure of ductus arteriosus)
- wound healing impairment
- thrombosis
- heart attack & stroke
